How do I simply create a mesh line?
Change your view to top orthographic (numpad 7 for top, numpad 5 to toggle perspective/ortho).
Add a plane (shift+A, select Mesh/plane in the menu).
Enter Edit Mode with Tab.
Select the 2 vertices on the right (R click to select, Shift+R Click to add to selection) and delete them with X and select "vertices" in the delete menu.
Now you can move your vertices where you need.

Select one and Ctrl+L Click to create one more where you click.

continue until you have your profile done.